Algorithm Worst Case Average Case Best Case Min. no. of swaps Max. no. of swaps
Bubble $\theta(n^{2})$ $\theta(n^{2})$ $\theta(n^{2})$ $\theta(n^{2})$ $\theta(n^{2})$
Selection $\theta(n^{2})$ $\theta(n^{2})$ $\theta(n^{2})$ 0 (when array is already sorted) $\theta(n^{2})$
Insertion $\theta(n^{2})$ $\theta(n^{2})$ $\theta(n)$ (when array is sorted) 0 (when array is already sorted) $\theta(n^{2})$
Quick $\theta(n^{2})$ (when array is sorted, and pivot taken from one end) $\theta(n\lg n)$ $\theta(n\lg n)$ 0 (when array is already sorted) $\theta(n^{2})$
Merge $\theta(n\lg n)$ $\theta(n\lg n)$ $\theta(n\lg n)$ Is not in-place sorting Is not in-place sorting
Heap $\theta(n\lg n)$ $\theta(n\lg n)$ $\theta(n\lg n)$ $O(n\lg n)$ $\theta(n\lg n)$

In-Place Sorting

When sorting happens within the same array, its called in-place sorting. All the above sorting except, merge sort are in-place sorting. In merge sort, we use an auxiliary array for merging two sub-arrays

Stable sorting

This matters only for arrays with same element repeated. If $A[x] = A[y]$, in the original array such that $x<y$, then in the sorted array, $A[x]$ must be placed at position $u$ and $A[y]$ must be placed at position $v$, such that $u<v$. i.e.; the relative positions of same value elements must be same in the sorted array as in the input array, for the sorting algorithm to be stable. In most cases stability depends on the way in which algorithm is implemented. Still, its not possible to implement heap sort as a stable sort.




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Algorithm Worst Case Average Case Best Case Min. no. of swaps Max. no. of swaps
Bubble $\theta(n^{2})$ $\theta(n^{2})$ $\theta(n^{2})$ $\theta(n^{2})$ $\theta(n^{2})$
Selection $\theta(n^{2})$ $\theta(n^{2})$ $\theta(n^{2})$ 0 (when array is already sorted) $\theta(n^{2})$
Insertion $\theta(n^{2})$ $\theta(n^{2})$ $\theta(n)$ (when array is sorted) 0 (when array is already sorted) $\theta(n^{2})$
Quick $\theta(n^{2})$ (when array is sorted, and pivot taken from one end) $\theta(n\lg n)$ $\theta(n\lg n)$ 0 (when array is already sorted) $\theta(n^{2})$
Merge $\theta(n\lg n)$ $\theta(n\lg n)$ $\theta(n\lg n)$ Is not in-place sorting Is not in-place sorting
Heap $\theta(n\lg n)$ $\theta(n\lg n)$ $\theta(n\lg n)$ $O(n\lg n)$ $\theta(n\lg n)$

In-Place Sorting[edit]

When sorting happens within the same array, its called in-place sorting. All the above sorting except, merge sort are in-place sorting. In merge sort, we use an auxiliary array for merging two sub-arrays

Stable sorting[edit]

This matters only for arrays with same element repeated. If $A[x] = A[y]$, in the original array such that $x<y$, then in the sorted array, $A[x]$ must be placed at position $u$ and $A[y]$ must be placed at position $v$, such that $u<v$. i.e.; the relative positions of same value elements must be same in the sorted array as in the input array, for the sorting algorithm to be stable. In most cases stability depends on the way in which algorithm is implemented. Still, its not possible to implement heap sort as a stable sort.




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